Near real time location and identification of subsurface chemical explosions using Gauribidanur Array data

This paper presents a near real time technique of event location and its identification as an earthquake or subsurface explosion using seismic Rg and Lg phases recorded at Gauribidanur Array (GBA). It is argued that the locations of local and regional seismic events having epicentral distances, Δ < 10o obtained using Rg and Lg phases are more accurate than those obtained using S-P time interval based on Jeffreys-Bullen (JB) travel time tables. Since the amplitude of Rg phase decreases rapidly with depth, its amplitude, for a given source strength, is expected to be higher for artificial sources like subsurface chemical explosions than that for natural earthquakes, whose foci are usually much deeper than that of chemical explosions. On the other hand the earthquake signals may be dominated by Lg phase which is not expected to be predominant in explosion signals. Thus, a discriminant based on the time domain amplitudes of Rg and Lg phases may be found which may separate the earthquake signals from chemical explosion signals. One such discriminant based on RMS amplitude ratio of Rg and Lg or Sg phase has been developed using GBA seismograms which effectively separates the chemical explosion signals from earthquakes in near online mode. (author)